1. Field of the Invention
The present invention relates to an engine valve operation mechanism comprising a timing transmission that is linked to a crankshaft and a cam system that has a cam linked to the driven side of the timing transmission and transmits the rotational force of the cam as opening and closing forces to intake and exhaust valves, the engine valve operation mechanism being provided in a valve operation chamber that is defined between a cylinder head and a head cover that is joined in an oil tight manner to the upper end of the cylinder head.
2. Description of the Prior Art
Such an engine valve operation mechanism is already known as disclosed in, for example, Japanese Patent Application Laid-open No. 8-177416.
With regard to such a conventional engine valve operation mechanism, an outer end of a support shaft that supports a cam is supported in a support hole provided in the outside wall of a cylinder head. In this case, in order to prevent oil leakage from the support hole, a sealing member that is in close contact with the inner periphery of the support hole is mounted around the outer periphery of the support shaft, and a stopper member such as a split pin for preventing the support shaft from becoming detached from the support hole is attached to the cylinder head. With such an arrangement, it is difficult to achieve a reduction in the number of components and the cost.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to provide an engine valve operation mechanism that can prevent oil leakage and detachment of the support shaft without employing a special sealing member and stopper member, to thereby contribute to a reduction in the cost.
In accordance with a first characteristic of the present invention in order to achieve the above-mentioned object, there is proposed an engine valve operation mechanism comprising a timing transmission that is linked to a crankshaft and a cam system that has a cam linked to the driven side of the timing transmission and transmits the rotational force of the cam as opening and closing forces to intake and exhaust valves, the engine valve operation mechanism being provided in a valve operation chamber that is defined between a cylinder head and a head cover that is joined in an oil tight manner to the upper end of the cylinder head, wherein opposite ends of a support shaft that supports the cam in a rotatable manner are supported in a first support hole of a first support wall formed in the cylinder head and a second support hole of a second support wall placed inwardly from the first support wall relative to the cylinder head, the first support hole is made as a through hole to allow the support shaft to be inserted into the first support hole and the second support hole from outside the cylinder head, and the inner face of the head cover prevents the support shaft from becoming detached from the first support hole.
In accordance with the above-mentioned first characteristic, since the support shaft that supports the cam by being inserted into the first support hole and the second support hole in that order is prevented from falling out by the inner face of the head cover that is joined to the cylinder head, it is unnecessary to provide a special stopper member for the support shaft. Moreover, since lubrication of the support shaft is carried out within the head cover and leakage of lubricating oil to the outside is prevented by the oil-tight joint between the head cover and the cylinder head, there is no need to attach a special sealing member to the support shaft. It is therefore possible to reduce the number of components to achieve a reduction in the cost.
Furthermore, in accordance with a second characteristic of the present invention, in addition to the above-mentioned first characteristic, there is proposed an engine valve operation mechanism wherein the first and second support walls are formed so that the first and second support holes are positioned above the plane in which the cylinder head and the head cover are joined, and the head cover is formed so that the head cover inner face is in contact with or in the vicinity of the outside face of the first support wall.
In accordance with the second characteristic, the head cover can be made compact while allowing the support shaft to be attached and detached prior to attaching the head cover.
Furthermore, in accordance with a third characteristic of the present invention, in addition to the above-mentioned first or second characteristic, there is proposed an engine valve operation mechanism wherein the second support hole is a bottomed hole, and both the bottom of the second support hole and the inner face of the head cover restrict the axial movement of the support shaft.
In accordance with the above-mentioned third characteristic, the axial movement of the support shaft can be restricted without employing a special positioning member so that the number of components can be further reduced.
The first and second support walls above correspond to a support wall 27 and a partition 85 in an embodiment of the present invention, which will be described below, the first and second support holes correspond to a through hole 28a and a bottomed hole 28b, and the valve operation chamber corresponds to first and second valve operation chambers 21a and 21b. 
The above-mentioned objects, other objects, characteristics and advantages of the present invention will become apparent from an explanation of a preferable embodiment which will be described in detail below by reference to the appended drawings.